So what we are left with is one person using 'you' and another using 'thou'. There are two possible explanations I can see:
- Gloucester represents the 'new' world - I don't know the play, so can't judge whether that 'fits'
- Lady Anne's 'thou' is a mark of respect, mimicking the system many languages have of a "V/T" system of personal pronouns. Languages that have a "V/T" system - like French, with vous and tu - use the tu form for children, servants, friends and family, and - paradoxically - royalty. I believe Gloucester is royal, in which case she's showing due deference. If he's not, maybe she regards his 'you' as rather too formal, and is using a form of address that implies 'you can treat me as a friend'* (or should that be 'thou can'st...'?)
In summary - there are lots of possibilities, and I don't really know! But well done for spotting the inconsistency.
PS * Unlikely, given the context. Maybe he's from a different faction (history isn't my strong point - check here http://en.wikipedia.org/wiki/Richard_III_(play) ) and has taken over where she used to have power (hence her 'Villain' - not a bad man then, but a servant). So her use of the familiar 'thou' has dramatic irony; she's using it to 'put him in his place', but the audience recognizes it as a sign that Gloucester will eventually become king.
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